Flash-based memory system with variable length page stripes including data protection information

ABSTRACT

Methods and apparatuses for enhanced protection of data stored in a FLASH memory system involve a controller capable of adapting to the failure of one or more FLASH memory devices in the memory system. The controller stores data in the form of page stripes, each page stripe composed of data pages, and each data page stored in a different FLASH memory device. The controller also detects failure of a FLASH memory device in which a data page of a particular page stripe is stored, reconstructs the data page, and stores the reconstructed data page in a new page stripe, where the number of data pages in the new page stripe is less than the number of data pages in the particular page stripe, and where no page of the new page stripe is stored in a memory location within the failed FLASH memory device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application for patent is a continuation of U.S. Non-Provisionalapplication Ser. No. 12/554,888, entitled “Method and Apparatus forAddressing Actual or Predicted Failures in a Flash-Based StorageSystem,” filed Sep. 5, 2009, and is also a continuation of U.S.Non-Provisional application Ser. No. 12/554,892, entitled “Flash-basedMemory System with Variable Length Page Stripes Including DataProtection Information,” filed Sep. 5, 2009, and is also a continuationof Non-Provisional application Ser. No. 12/971,286, entitled “Method andApparatus for Protecting Data Using Variable Size Page Stripes in aFlash-Based Storage System,” filed Dec. 17, 2010, which is a divisionalof U.S. Non-Provisional application Ser. No. 12/554,891 (now U.S. Pat.No. 7,856,528), entitled “Method and Apparatus for Protecting Data UsingVariable Size Page Stripes in a Flash-Based Storage System,” filed Sep.5, 2009, which claims priority to U.S. Provisional Application Ser. No.61/232,913, entitled “Method and Apparatus for Efficient and EnhancedProtection, Storage and Retrieval of Data Stored in Multiple FlashStorage Locations,” filed Aug. 11, 2009, the foregoing applicationsincorporated herein by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

REFERENCE TO APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure relates generally to methods and apparatus for improvingthe ability of a memory storage system to efficiently and effectivelyprotect, store and retrieve data stored in multiple storage locations.

2. Description of the Related Art

In certain memory storage systems data is stored in multiple storagelocations. For example, in some such systems, multiple individual harddisks or memory chips are used to store data and the data stored in oneor more of the storage devices is associated with data stored in otherstorage devices in such a manner that data errors in one or more storagedevices can be detected and possibly corrected. One such approach is tostore a given quantity of data across multiple storage locations bydividing the data into data portions of equal length—the individual dataportions sometimes being referred to as “data pages”—and then storingthe data pages in multiple storage locations such that one data page isstored in each storage device. In connection with this approach, afurther storage device may be used to store a page of data protectioninformation, where a given page of data protection information isassociated with a specific set of data pages stored in the multiplestorage locations. In some instances, the set of data pages in themultiple locations that is used to store associated data is referred toas a “data stripe” or “Page Stripe.”

In conventional systems, the length of all of the data stripes used inthe system is the same. Thus, in such systems, all of the data stored inthe system is divided into data stripes of the same length, with eachdata stripe consisting of the same number of pages, and with each datastripe being stored in the same number of memory locations. Also, insuch system, each data stripe conventionally utilizes the same form ofdata protection and the data protection information for each data stripeis determined in the same way.

In conventional systems as described above, if there is a full orcomplete failure of the structure associated with a given memorylocation (e.g., the specific memory device associated with that locationfails), the data protection information for a given data stripe canoften be used to reconstruct the data in the data page that was storedin the failed memory location. Using the reconstructed data, the datafor the entire data stripe may be reconstructed. In such systems, when astorage location in a system as described fails and the data protectioninformation page is used to reconstruct the data associated with thefailed storage location, the reconstructed data is stored in a reserveor back-up storage location that takes the place of the failed storagelocation within the system such that the data stripe that was associatedwith the failed memory location is reconstructed in substantially thesame form. Thus, the reconstructed data stripe consists of the samenumber of pages, is stored in the same number of memory locations, andutilizes the same form of data protection as the data stripe that wasassociated with the failed storage location.

While the conventional approach described above can beneficially detectand respond to the failure of a memory storage location within a memorystorage system, it requires the availability of a reserve or back-upstorage location to take the place of the failed storage location. Suchreserve or back-up locations can be costly and/or inefficient to provideand/or maintain and/or are not always available.

SUMMARY OF THE INVENTION

The disclosed embodiments are directed to methods and apparatuses forproviding efficient and enhanced protection of data stored in a FLASHmemory system. The methods and apparatuses involve a system controllerfor a plurality of FLASH memory devices in the FLASH memory system thatis capable of protecting data using different size page stripes. In someembodiments, the system controller is configured to store data in theFLASH memory devices in the form of page stripes, each page stripecomprising a plurality of pages of information, each page of informationbeing stored in a FLASH memory device that is different from each of theFLASH memory devices in which the other pages of information within thepage stripe are stored. The system controller stores the data in amanner such that the pages making up each page stripe include aplurality of data pages and at least one data protection page containingdata protection information that may be used to reconstruct data storedin a data page within the page stripe that becomes corrupted orunavailable, with the data protection information for a given pagestripe being obtained by performing a bitwise logical operation on theinformation within the data pages for the given page stripe. In oneimplementation, the page stripes stored by the system controller includea first page stripe having N data pages and one data protection page,and a second page stripe having M data pages and one data protectionpage, where N is an integer greater than three and M is an integer lessthan N.

In some embodiments, the system controller is configured to write datato the FLASH memory devices in a striped fashion using data stripes,where each data stripe includes a group of data collections and anassociated set of data protection information. The system controllerwrites the data in a manner such that each data collection within agroup of data collections is written into a FLASH memory device thatdiffers from the FLASH memory devices into which the other datacollections within the group of data collections and the data protectioninformation associated with the group of data collections are written,each data collection includes error correction code data generated fromthe data stored in the data collection, and each set of data protectioninformation is generated by performing a bitwise exclusive-or (XOR) ofthe data within the data collections associated with the set of dataprotection information. The system controller may then identify an errorwithin the data collection using the error correction code data withineach data collection and reconstruct the data for a data collectionassociated with the set of data protection information using the set ofdata protection information, where the number of data collections withinthe group of data collections can be varied.

In some embodiments, the system controller is configured to writeinformation to the FLASH memory devices using data stripes such that afirst data stripe has M data pages and a data protection page, where Mis an integer greater than three and where information stored in thedata protection page for the first data stripe was generated through theperformance of a given operation on information stored within the M datapages of the first data stripe. The controller is further configured towrite a second data stripe having N data pages and a data protectionpage in the FLASH memory devices, where N is an integer less than M, andwherein information stored in the data protection page for the seconddata stripe was generated from the performance of the given operation oninformation stored within the N data pages of the second stripe.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the disclosed embodiments willbecome apparent from the following detailed description and uponreference to the drawings, wherein:

FIG. 1 illustrates an exemplary FLASH memory storage system inaccordance with the present disclosure;

FIGS. 2A and 2B illustrate an exemplary arrangement of physical memorywithin a FLASH memory chip in accordance with the present disclosure;

FIGS. 3A-3F illustrate exemplary implementations of Page Stripes inaccordance with the present disclosure;

FIG. 4 illustrates an exemplary Data Page in accordance with the presentdisclosure;

FIG. 5 illustrates an exemplary Data Protection Page in accordance withthe present disclosure;

FIG. 6 illustrates an exemplary circuit that can be used to produce aData Protection Page in accordance with the present disclosure;

FIGS. 7A and 7B illustrate an exemplary Page Stripe and an exemplarystorage arrangement for the Page Stripe in accordance with the presentdisclosure;

FIGS. 8A and 8B illustrate another exemplary Page Stripe and anotherexemplary storage arrangement therefor in accordance with the presentdisclosure;

FIGS. 9A-9D illustrate additional exemplary Page Stripes and additionalexemplary storage arrangements therefor in accordance with the presentdisclosure;

FIGS. 10A-10D illustrate further exemplary Page Stripes and furtherexemplary storage arrangements therefor in accordance with the presentdisclosure;

FIG. 11 illustrates an exemplary arrangement of Data Pages within groupsof Blocks in accordance with the present disclosure;

FIG. 12 illustrates an exemplary arrangement of Data Pages within groupsof Blocks where data pages that already contain data are indicated asunavailable in accordance with the present disclosure;

FIG. 13 illustrates an exemplary Ready-to-Erase buffer in accordancewith the present disclosure;

FIGS. 14A-14D illustrate another exemplary FLASH memory storage systemand exemplary storage arrangement where memory chips that have failedare indicated as unavailable in accordance with the present disclosure;and

FIGS. 15A and 15B illustrate an exemplary Logical-to-PhysicalTranslation Table having Data Identifiers therein in accordance with thepresent disclosure.

DETAILED DESCRIPTION

The figures described above and the written description of specificstructures and functions below are not presented to limit the scope ofwhat Applicants have invented or the scope of the appended claims.Rather, the figures and written description are provided to teach anyperson skilled in the art to make and use the inventions for whichpatent protection is sought. Those skilled in the art will appreciatethat not all features of a commercial embodiment of the inventions aredescribed or shown for the sake of clarity and understanding. Persons ofskill in this art will also appreciate that the development of an actualcommercial embodiment incorporating aspects of the present inventionswill require numerous implementation-specific decisions to achieve thedeveloper's ultimate goal for the commercial embodiment. Suchimplementation-specific decisions may include, and likely are notlimited to, compliance with system-related, business-related,government-related and other constraints, which may vary by specificimplementation, location, and from time to time. While a developer'sefforts might be complex and time-consuming in an absolute sense, suchefforts would be, nevertheless, a routine undertaking for those of skillin this art having benefit of this disclosure. It must be understoodthat the inventions disclosed and taught herein are susceptible tonumerous and various modifications and alternative forms. Lastly, theuse of a singular term, such as, but not limited to, “a,” is notintended as limiting of the number of items. Also, the use of relationalterms, such as, but not limited to, “top,” “bottom,” “left,” “right,”“upper,” “lower,” “down,” “up,” “side,” and the like are used in thewritten description for clarity in specific reference to the figures andare not intended to limit the scope of the invention or the appendedclaims.

Exemplary Memory System:

Turning to the drawings and, in particular, to FIG. 1 a memory storagesystem 100 in accordance with certain teachings of the presentdisclosure is illustrated. While it can be constructed in various ways,the memory storage system exemplified in FIG. 1 is constructed on asingle multi-layer printed circuit board.

The exemplary illustrated memory storage system 100 includes: a Flashcontroller 10; Flash controller memory 11; a CPU 15; CPU memory 17; anexternal communication bus 12 used to communicate information to theFlash controller 10; a Flash memory storage array 14; and an internalcommunication bus 16 that enables communications between the Flashcontroller 10 and the Flash memory storage array 14. In the illustratedexample, the components of the memory storage system 100 are mounted tothe same printed circuit board. Such mounting may be accomplishedthrough, for example, surface mounting techniques, through-holetechniques, through the use of sockets and socket-mounts and/or othermounting techniques.

The Flash controller 10 may take many forms. In the example of FIG. 1,the Flash controller 10 is a field programmable gate array (FPGA) that,during start-up of the system, is programmed automatically with aprogram stored in nonvolatile memory within Flash controller 10.Although the FPGA programs itself automatically during system start-up,it may also be configured by the CPU 15.

Like Flash the controller 10, the controller memory 11 may take manyforms. In the exemplary embodiment of FIG. 1, the controller memory 11takes the form of random access memory and in particular DDR2 RAMmemory. Such RAM memory is an example of “volatile” memory, or memorythat requires a source of power to maintain the integrity of theinformation stored within the memory.

The communication bus 12 can be any acceptable data bus forcommunicating memory access requests between a host device (such as apersonal computer, a router, etc.) and the memory system 100. Thecommunication bus 12 can also use any acceptable data communicationprotocols.

In general operation, the Flash controller 10 receives requests viacommunication bus 12 to read data stored in the Flash memory storagearray 14 and/or to store data in the Flash memory storage array 14. TheFlash controller 10 responds to these requests either by accessing theFlash memory storage array 14 to read or write the requested data fromor into the storage array 14 in accordance with the request, byaccessing a memory cache (not illustrated) associated with the storagearray 14, or by performing a read or write operation through the use ofa Data Identifier as described in more detail below.

The Flash memory storage array 14 may take many forms. In theillustrated example, the Flash memory storage array 14 is formed fromtwenty individually addressable Flash memory storage devices dividedinto groups of two (0 a, 0 b), (1 a, 1 b), (2 a, 2 b), through (9 a, 9b). In the illustrated example, each of the Flash memory storage devices0 a-9 b takes the form of a board-mounted Flash memory chip, such as,for example, a 64 Gigabit (Gb) Single Level Cell (SLC) NAND flash memorychip. Flash memory is an example of “non-volatile” memory, or memorythat does not require a source of power to maintain the integrity of theinformation stored within the memory.

The internal communication bus 16 can take any form that enables thecommunications described herein. In the example of FIG. 1, this bus 16is formed from ten individual eight-bit communication buses 0-9 (notindividually illustrated), each arranged to enable communication betweenthe Flash controller 10 and each of the groups of two memory storagedevices 0 a-9 b. Thus, for example, communication bus 0 enablescommunications between the Flash controller 10 and the group comprisingmemory devices 0 a and 0 b, and communication bus 4 enablescommunications between the Flash controller 10 and the memory devices 4a and 4 b.

Referring to FIG. 1, an on-board ultra-capacitor 18 may also be providedand configured to receive charge during intervals when power is suppliedto the Flash memory system 100 and to provide power for a limited timeto the components making up the Flash memory system 100 whenever appliedpower is removed or drops below the power level provided by theultra-capacitor. The purpose of the ultra-capacitor is to provide powerfor limited operation of the Flash memory system 100 upon the failure ofpower to the system. In the event of a power loss, the ultra-capacitorwill automatically engage and provide power to most or all components ofthe Flash memory system 100. In the Flash system of FIG. 1, theultra-capacitor is sized to provide adequate power to allow the systemto store into the Flash memory array 14 any data that may be retained inthe volatile RAM storage device 11 at the time of power loss or powerfailure, as well as any other volatile information that may be necessaryor useful for proper board operation. In that manner, the overall Flashsystem 100 acts as a non-volatile memory system, even though it utilizesvarious volatile memory components. Alternate embodiments are envisionedwhere multiple ultra-capacitors at various distributed locations acrossthe printed circuit board and/or a single ultra-capacitor bank is usedto provide the described back-up power. As used herein, the termultra-capacitor is any capacitor with sufficiently high capacitance toprovide the back-up power required to perform the functions describedabove that is adequately sized to fit on a printed circuit board and beused in a system, such as system 100.

The system 100 uses an addressing scheme to allow the Flash controller10 to access specific memory locations within the memory array 14. Forpurposes of explanation, this addressing scheme will be discussed in thecontext of a WRITE request, although it will be understood that the sameaddressing scheme can be and is used for other requests, such as READrequests.

In general, the Flash controller 10 will receive a WRITE request from ahost device that contains both: (i) data to be stored in the memorysystem 100, and (ii) an indication of the memory address where the hostdevice would like for the data to be stored. The WRITE request may alsoinclude an indication of the amount (or size) of the data to betransferred. In one embodiment, the system is constructed such that theamount of data (or the size of each WRITE request) is fixed at the sizeof a single Flash memory page. In the exemplary embodiment of FIG. 1,this corresponds to 4 KB (Kilobytes) of information. In such anembodiment, the address provided by the host device can correspond tothe address of a Page within a logical address space.

In the system 100 of FIG. 1, the address received by the Flashcontroller 10 does not refer to an actual physical location within thememory array 14. Instead, the address received by the Flash controller10 from the host device is a Logical Block Address (or “LBA”) because itrefers to a logical address for a given Flash memory page, rather thanto any specific physical location within the memory array 14. Theconcept of Logical Block Addressing as used in the system 100 of FIG. 1is discussed in more detail below.

In the system 100 of FIG. 1, the memory array 14 comprises a collectionof individual Flash memory storage chips. A specific physical addressingscheme is used to allow access to the various physical memory locationswithin the Flash memory chips 0 a-9 b. In the embodiment of FIG. 1, thisphysical addressing scheme is based on the physical organization andlayout of the memory array 14.

Referring to FIG. 1, as noted earlier, the physical memory chips 0 a-9 bthat make up the memory array 14 are divided into ten groups of twochips. For purposes of the physical addressing scheme, each group of twochips forms a “Lane,” also sometimes referred to as a “Channel,” suchthat there are ten Lanes or Channels within the memory array 14(LANE0-LANE9). LANE0 corresponds to chips 0 a and 0 b; LANE1 to chips 1a and 1 b and so on, with LANE9 corresponding to chips 9 a and 9 b. Inthe embodiment of FIG. 1, each of the individual Lanes has associatedwith it one of the individual eight-bit buses 0-9 mentioned earlier toenable the Flash controller 10 to communicate information across theLane. Thus, by directing its communications to one of the specificcommunication buses 0-9, the Flash controller 10 can direct itscommunications to one of the Lanes of memory chips. Because eachcommunication bus 0-9 for a given Lane is independent of thecommunication buses for the other Lanes, the Flash controller 10 canissue commands and send or receive data across the various communicationbuses at the same time such that the Flash controller can access thememory chips corresponding to the individual Lanes at, or very nearlyat, the same time.

In the addressing scheme for the memory system 100 of FIG. 1, each Laneenables communications with one of two physical memory chips at anygiven time. Thus, for example, data provided across communication bus 0can enable communications with either chip 0 a or chip 0 b. In theembodiment of FIG. 1, for Lane 0 as an example, the Flash controller 10controls eight individual chip enable lines (four for chip 0 a and fourfor chip 0 b) so that each chip and its corresponding internal hardwareresources may be addressed individually. The assertion of a single chipenable line results in communications with one chip and one chip enable(“CE”) resource within that chip.

In the embodiment of FIG. 1, the physical memory locations within eachof the Flash memory chips are divided into physical locations that canbe addressed and/or identified through the use of one or more of: ChipEnables (“CEs,” generally described above); Dice (multiple individualdie); Planes; Blocks; and Pages. This exemplary addressing scheme isgenerally illustrated in FIGS. 2A and 2B.

FIGS. 2A and 2B generally illustrate the physical memory 200 within eachof the individual Flash memory chips 0 a-9 b of FIG. 1. Referring toFIGS. 2A and 2B, it may be noted that, at one level, the physical memory200 within the device may be divided into four high level groupings,where each grouping has associated with it an individual Chip Enable (or“CE”) line. In the example of FIG. 2, the physical memory 200 of eachFlash chip is divided into four groupings of Chip Enables (CE0, CE1, CE2and CE3) and each Chip Enable would have a separate CE line. During anaddressing state, the activation of one of the four CE lines will enableaccess to or from memory locations within the group of memory locationsassociated with the asserted CE line.

In the embodiment of FIGS. 2A and 2B, each CE group of memory locationsis further divided into Dice (multiple individual die), Pages, Blocksand Planes.

The division of the physical memory into Dice is generally related tothe manner in which the structures internal to the chip are formed. Inthe exemplary embodiment of FIG. 2A, each Chip Enable includes two Dice(DIE0 and DIE1) which are illustrated for CE0-CE3.

In the addressing scheme of FIGS. 2A and 2B, a Page is the smallestindividually addressable data unit. In the exemplary system, each Pageof data has a specific length which in the example is a data lengthcorresponding to 4 KB of data plus 128 additional bytes used asdescribed in more detail below. In the embodiment of FIG. 1, data iswritten into or read from the memory array 14 on a Page-by-Page basis.

In the system of FIGS. 2A and 2B, the various Pages of data are groupedtogether to form “Blocks.” In general, a Block is a collection of pagesthat are associated with one another, typically in a physical manner.The physical association is such that the Block is the smallest group ofFlash memory locations that can be erased at any given time. In theembodiment of FIGS. 2A and 2B, each Block includes 64 Pages of data.This is reflected generally in FIG. 2B.

When dealing with Flash memory, an ERASE operation involves theplacement of all of the memory locations that are subject to the eraseoperation in a particular logical state, corresponding to a specificphysical state of the memory locations. In the embodiment of FIG. 1, theERASE operation is performed on a Block-by-Block basis and theperformance of an ERASE operation of a given block places all of thememory locations within the Block into a logical “1” state,corresponding to a state where there is no or relatively low chargestored within the storage devices associated with each memory location.Thus, while data may be read from or written to the memory array 14 on aPage-by-Page basis, the memory locations can be erased only on aBlock-by-Block basis in the embodiment shown.

In the arrangement of FIGS. 2A and 2B, the Blocks of data are groupedtogether to form “Planes.” Each Plane represents a collection of Blocksthat, because of the physical layout of the Flash memory chips, arephysically associated with one another and that utilize common circuitryfor the performance of various operations. In the example of FIGS. 2Aand 2B, each Die includes two Planes and each Plane comprises 2048Blocks of data. In FIG. 2A, the Blocks within the Planes are illustratedfor CE3.

In the illustrated example, the various Blocks of data that form a givenPlane utilize common circuitry within the individual chips 0 a-9 b toperform certain operations, including READ and WRITE operations. Thus,for example, each of the Pages of Data within an exemplary Plane (e.g.,PLANE0 of DIE0 of CE3) will be associated with some specificinput/output circuitry that includes an Input/Output (I/O) Buffer. TheI/O Buffer is a buffer that is sized to store at least one Page of data.When data is to be written into a specific Page in a Block, a Page ofdata is first written to the I/O Buffer for the Plane, and the Page ofdata is then written into the memory locations associated with thespecific Page. Similarly, when a specific Page of data is to be readfrom a location within the Plane, the Page of data is first retrievedfrom the specific Page to be accessed and placed in the I/O Buffer forthe Plane in which the accessed Page resides. If the data was requestedin a manner where it would be accessible outside the Flash chip 200, thedata is delivered from the I/O Buffer in the associated Plane to theFlash controller 10.

The memory system 100 of FIG. 1 does not generally allow devicesexternal to the system to directly address and access the physicalmemory locations within the Flash memory storage array. Instead, thememory system 100 is generally configured to present a single contiguouslogical address space to the external devices that may request READ orWRITE access to data stored in the memory array 14. The use of thislogical address space allows the system 100 to present a logical addressspace external to the system 100, such that a host device can write datato or read data from logical addresses within the address space—thusallowing easy access and use of the memory system 100—but also allowsthe Flash controller 10 and CPU 15 to control where the data that isassociated with the various logical addresses is actually stored in thephysical memory locations that make up memory array 14 such that theperformance of the system is optimized.

Because the system 100 isolates the logical address space made availableto host devices from the physical memory within the array 14, it is notnecessary that the size of the physical memory array 14 be equal to thesize of the logical address space presented externally to the system. Insome embodiments it is beneficial to present a logical address spacethat is less than the total available address space. Such an approachensures that there is available raw physical memory for systemoperation, even if data is written to each presented logical addressspace. For example, in the embodiment of FIG. 1, where the Flash memoryarray 14 is formed using 64 Gb Flash memory chips providing a rawphysical memory space of 1280 Gb of storage, the system could present alogical address space corresponding to approximately 896 Gb of datastorage.

Page Stripes:

In the exemplary system of FIG. 1, data is written to the memory array14 using associated Pages of data known as “Page Stripes.” In theillustrated embodiment, a Page Stripe represents a grouping ofassociated information, stored in a particular manner within the memoryarray 14.

Page Stripes—Information Content:

While the specific information that is stored in a given Page Stripe canvary, in one embodiment each Page Stripe includes a number of Pages ofstored data (typically provided by a host device) and one Page of dataused to protect the stored data. While the actual size of a Page Stripemay vary, for purposes of the following discussion an exemplary PageStripe consisting of nine pages of stored data and one page of dataprotection information is described.

FIG. 3A illustrates an exemplary Page Stripe 300 in accordance with theteachings of the present disclosure. Referring to FIG. 3A, the exemplaryPage Stripe consists of nine pages of data, each referred to herein as a“Data Page” (DPAGE0, DPAGE1, DPAGE2 . . . DPAGE8 in the example) and onepage of data protection information, referred to herein as a “DataProtection Page” (PPAGE9 in the example).

FIG. 4 generally illustrates the format used for each Data Page withinthe Page Stripe 300. Referring to FIG. 4, an exemplary Data Page 410 isillustrated. The illustrated Data Page 410 includes 4096 bytes of storeddata and 128 bytes of additional information that, in the illustratedexample, includes a number of bits that provide the Logical BlockAddress (LBA) corresponding to the specific Data Page at issue; a numberof bits that reflect a cyclic redundancy check (CRC) of the combinationof the stored data and the stored LBA; and a number of Error CorrectionCode (ECC) bits. In the illustrated example, the ECC bits are calculatedfrom a combination of the stored data bytes, the LBA bits and the CRCbits. In some embodiments, bits of data reflecting the status of theBlock in which the illustrated Page is found may also be stored withinthe Data Page.

In the example of FIG. 4, the LBA information is in the form of fourbytes of data, although the length of the LBA address is not criticaland can vary.

The CRC data can take many forms and be of variable length and varioustechniques may be used to determine the CRC data associated with the LBAaddress stored in the Data Page. In one example, the CRC data comprisesa 64-bit value formed by a hashing technique that performs a hashoperation on the 4096 data bytes plus the four LBA data bytes to producea 64-bit CRC hash value.

Various techniques may be used to determine the ECC bits for the storeddata and LBA information stored in the Data Page 410.

In one embodiment, the ECC data associated with the stored data and LBAinformation is calculated using a beneficial technique in which the ECCdata stored in the Data Page comprises thirty-three sixteen-bit ECCsegments: each of thirty-two of the ECC segments are associated with 128unique bytes of the 4 KB data area, and a thirty-third ECC segment isassociated with the LBA and CRC fields.

FIG. 5 generally illustrates the form of the information stored in theData Protection

Page of the exemplary Page Stripe 300. Referring to FIG. 5, an exemplaryData Protection Page 500 is illustrated. The data and LBA fields of theData Protection Page 500 simply contain the bit-by-bit Exclusive Or(XOR) of the corresponding fields in one or more of the associated DataPages (DPAGE0, DPAGE1, DPAGE2 . . . DPAGE8). The ECC and CRC fields forthe Data Protection Page 500 are recalculated for the Data ProtectionPage 500 in a manner identical to that used in the corresponding DataPages. The XOR calculation used to produce the Data Protection Page canbe accomplished using the apparatus of FIG. 6 and/or a softwareapproach.

Referring to FIG. 6, XOR circuitry 600 is disclosed that includes aninput memory buffer 60, an addressable XOR memory buffer 61, a multi-bitXOR circuit/buffer 63 and a multiplexer (MUX) 64. ECC and CRCcalculation logic 65 is also illustrated, as is the physical Flashmemory array 66. In the illustrated embodiment, each of the input buffer60, XOR buffer 61, XOR circuit 63 and MUX 64 operate on a Page ofinformation.

The circuitry 600 of FIG. 6 operates as follows. Data destined for theFlash memory 66 passes first through input memory buffer 60. If thisdata is the first Page of a new Page Stripe, the data is copied directlyinto the addressable XOR memory buffer 61 as it flows into thedownstream ECC and CRC calculation logic 66. For the second andsubsequent Pages of a Page Stripe, previous data in the addressable XORmemory buffer is unloaded and XORed with new data as the new data isunloaded from the input memory buffer 60. The result is then writtenback into the addressable XOR memory buffer 61, yielding the XOR of allData Pages up to and including the current one. This operation isrepeated until the data in the addressable XOR memory buffer 61 reflectsthe XOR of the data in the Data Pages that make up the Page Stripe atissue, after which the addressable XOR memory buffer 61 is written toFlash memory. Multiplexer 64 selects between current data and theresulting XOR calculation.

The XOR operation may alternately be performed through the use ofsoftware or firmware.

It may be noted that through the use of the Page format described abovein connection with FIG. 4 and the use of the Data Protection Page 500 ofFIG. 5, the data that is stored in a Page Stripe as described herein isprotected through multiple different protection mechanisms. First, theuse of the ECC bits in each Data Page allows the correction of anysingle bit error and the detection of any double bit error within eachgroup of 128 data bytes. ECC also allows the same single-bit errorcorrection and double-bit error detection within the LBA and CRC fields.After ECC checking and correction is performed, the corrected CRC fieldis used to validate the corrected data. Used together, these twomechanisms allow for the correction of relatively benign errors and thedetection of more serious errors using only local “intra-Page”information. Should an uncorrectable error occur in a Flash Page, thedata and LBA information from the failing Page may be reconstructed fromthe other Pages (including the XOR Data Protection Page) within the samePage Stripe using the information in the Data Protection Page for thePage Stripe. Note that the XOR Data Protection Page for each Page Stripeemploys the same local protection mechanisms (ECC and CRC) as everyother Data Page within the Page Stripe.

The specific Page Stripe 300 of FIG. 3A is but one example of a PageStripe in accordance with the teachings of this disclosure. Page Stripesof different sizes and constructions can also be used. One suchalternate Page Stripe is reflected in the embodiment of FIG. 3B. FIG. 3Billustrates an alternate Page Stripe 340 that includes only nine totalPages of data with eight of the Pages (DPAGE0-DPAGE7) being Data Pagesand one of the Pages (PPAGE8) being a Data Protection Page. In theillustrated embodiment of FIG. 3B, the individual Data Pages(DPAGE0-DPAGE7) are constructed in accordance with the Data Page formatof FIG. 4 and the Data Protection Page is of the form reflected in FIG.5. Because the Page Stripe 340 includes only eight Data Pages, however,the Data Protection Page (PPAGE8) will include the XOR of only eightData Pages, as opposed to the nine Data Pages that would be used for thePage Stripe 300 of FIG. 3A.

FIG. 3C illustrates yet another Page Stripe 350, in accordance with theteachings of the present disclosure. Page Stripe 350 includes only eighttotal pages, with seven of the Pages (DPAGE0-DPAGE6) being Data Pagesand One of the Pages (PPAGE7) being a Data Protection Page.

In the exemplary system 100 disclosed herein, it is not necessarilyrequired to have the Data Protection Page be located as the last page ofa given Page Stripe. The Data Protection Page can be located at any ofthe Page locations within the Page Stripe. As one example of such a PageStripe, FIG. 3D illustrates a Page Stripe 360 that is formed from atotal of ten Pages of information, where the Data Protection Page islocated at the PPAGE4 location. As an alternate example, FIG. 3Eillustrates a Page Stripe 370 with ten Pages of information includingnine Data Pages and a Data Protection Page at the PPAGE7 location. FIG.3F illustrates yet another example, depicting a Page Stripe 380 havingeight Pages, including Seven Data Pages and one Data Protection Page atthe PPAGE0 location.

Page Stripes—Storage Format:

While the memory locations in which the Pages of data within a PageStripe can be stored may vary within memory array 14, in one embodiment,the Pages that make up a given Page Stripe are stored in physical memorylocations selected in such a manner that the overall operation of thememory system 100 is optimized. In this embodiment, the physical memorylocations in which the data in each Page Stripe is stored are such thatthe physical Lane associated with each Page of data within the PageStripe is different from the Lanes associated with the other Pages thatmake up the Page Stripe. As generally reflected in FIG. 7A, thisembodiment allows for efficient writing and reading of a Page Stripe tothe memory array since it allows the Pages of data that make up the PageStripe to be written to the memory array 14 simultaneously ornear-simultaneously by having the Flash controller 10 issue commands tothe various Lanes at, or close to, the same time.

FIG. 7A illustrates an exemplary Page Stripe 700 consisting of nine DataPages 70 a, 70 b, 70 c through 70 i and one Data Protection Page 70 j.FIG. 7B illustrates the manner in which this Page Stripe 700 can bestored in the memory array 14 of FIG. 1.

In the example of FIG. 7B, the first Data Page 70 a is stored in aphysical memory location within LANE0; the second Data Page 70 b isstored in a physical memory location within LANE1; the third Data Page70 c is stored in a physical memory location within LANE2, and so onuntil the ninth Data Page 70 i is stored in a physical memory locationwithin LANE8. The Data Protection Page 70 j is stored in a physicallocation within LANE9.

Because the various Pages that make up the exemplary Page Stripe 700 arestored as illustrated in FIG. 7B, and because there are independentcommunication lines between the Flash controller 10 and each of thevarious Lanes, the Pages associated with Page Stripe 700 can be writtento or read from the memory array 14 simultaneously ornear-simultaneously. This arrangement allows for relatively quick readand write operations and allows data to be stored to and retrieved fromthe memory array 14 in an efficient and effective manner.

It should be noted that the example of FIGS. 7A and 7B is but oneexample of how a Page Stripe can be stored within the physical memoryarray. FIGS. 8A and 8B illustrate an alternate arrangement.

FIG. 8A illustrates an exemplary Page Stripe 800 that includes eightData Pages 80 a-80 h and a single Data Protection Page 80 i. FIG. 8Billustrates an example of how the Pages making up Page Stripe 800 can bestored in the memory array 14. In the illustrated example, the firstData Page 80 a is stored in a physical location associated with LANE0,the second Data Page 80 b with a physical location associated with LANE1and the third Data Page 80 c in a physical location within LANE2. Notehowever, that there is no Data Page stored within any physical locationassociated with LANE3. The fourth through eighth Data Pages (80 d-80 h)are then stored in physical locations within LANE4-LANE8, respectively,and the Data Protection Page 80 i is stored within a location in LANE9.This example illustrates the fact that in the illustrated embodiment,while each Page of data within a Page Stripe is stored in a locationassociated with a Lane that differs from the Lane associated with thestorage locations of each other Page within the Page Stripe, it is notnecessary that data for a Page Stripe be stored in locations within eachLane. For Page Stripes that include a number of Pages that is less thanthe number of Lanes of a given memory array, there will be one or moreLanes in which no data within the Page Stripe is stored.

In each of the examples of FIGS. 7A-7B and 8A-8B, the Pages that make upthe exemplary Page Stripes are stored sequentially across the Lanes,such that each of the Lane designations for the memory locationsassociated with the Pages within the Page Stripe are sequential as oneconsiders the Page Stripe from the first Data Page to the Second DataPage continuing to the Data Protection Page. While this approach is notcritical to the disclosed embodiments, it is beneficial in that it cansimplify the implementation of the disclosed subject matter.

While there may be benefits to having the Pages associated with a givenPage Stripe stored sequentially across the available Lanes, it is notcritical that the Pages within a Page Stripe be written in anyparticular order. In some embodiments, Page Stripes are stored such thatthe Pages associated with the Page Stripe are written sequentiallyacross the Lanes, but with the first Data Page of the Page Stripewritten into a physical location associated with a Lane other thanLANE0. These embodiments are illustrated in FIGS. 9A-9D below.

FIGS. 9A-9D illustrate examples of how an exemplary Page Stripe 900containing nine Data Pages 90 a-90 i and a single Data Protection Page90 j can be written sequentially across Lanes within memory array 14with the first Data Page being stored in a location associated with aLane other than LANE0. For example, in FIG. 9B, Page Stripe 900 isstored sequentially with the first Data Page stored at an addressassociated with LANE3 and the Page Stripe sequentially “wrapping around”such that the Data Protection Page 90 j is stored in an addressassociated with LANE2. FIG. 9C illustrates storage with the first DataPage 90 a in an address associated with LANE4 and FIG. 9D illustratesstorage with the first Data Page 90 a in an address associated withLANE5.

FIGS. 10A-10D illustrate still further examples of how a Page Stripe1000 including eight Data Pages and a single Data Protection Page can bewritten into memory array 14. In general, Pages within a particular PageStripe may be written to various Lanes, in any order, so long as no twoPages of the same Page Stripe occupy the same Lane.

Memory System—Exemplary Operations:

Having described the general physical structure of the memory system 100and aspects of the manner in which data in the form of Page Stripes isaddressed and stored within the memory array 14, certain operationalaspects of the system 100 will be described including aspects relatingto the WRITING and READING of data to and from the system.

Exemplary WRITE Operations:

At a high level, and in general, the exemplary system of FIG. 1 mayperform WRITE operations through a number of steps including:

(1) receiving from a host device data, typically in the form of a Pageof data, to be stored in memory along with a Logical Block Address (LBA)at which the host device would like for the data to be stored;

(2) determining whether the LBA for the received data was previouslyassociated with one or more different physical memory Pages and, if so,changing the status of the previous Page or Pages of memory to indicatethat the previously stored data is no longer valid; and

(3) identifying an available Page within a Page Stripe where thereceived data can be stored;

(4) configuring the received data such that it is divided into a datagroup that fits within the identified Page Stripe on a Page-alignedbasis (i.e., data that can be written into a Page or a Page Stripe on aPage-by-Page basis);

(5) writing the data into the available Page;

(6) updating a table associating Logical Addresses from the host devicewith physical addresses in the memory array to associate the physicalPage where the data was stored with the LBA provided by the host device.

It is not critical that these operations be performed in the describedorder.

The step of receiving, from a host device, data to be stored and an LBAwhere the host device would like for the data to be stored is relativelystraightforward. For the embodiment of FIG. 1, the data and the LBAsupplied by the host are typically provided to the System Controller 10over the communication bus 12.

The step of determining whether the LBA for the received data waspreviously associated with one or more different physical memory Pagesand, if so, changing the status of the previous Page or Pages of memoryto an indication that the data is no longer valid (a DIRTY indication)involves the Flash controller 10 comparing the received LBA to the LBAentries in the Logical-to-Physical conversion tables. If the comparisonindicates that the LBA provided by the host device for the current WRITEoperation was previously associated with another physical memorylocation, then the system will know that the previously stored data isno longer valid. Accordingly, the system will change a status indicatorfor the physical Pages of data associated with the previously storeddata to indicate that they are DIRTY, or no longer VALID.

The step of identifying one or more available Pages where the receiveddata can be stored can be implemented in a variety of ways. In manyinstances, the Flash controller will already be in possession ofinformation that identifies a specific group of associated Blocks inphysical memory that are available to store data. In such instances, theFlash controller 10 will then have an internal count indicating whichPages within the group of Blocks already have data stored therein andwill use the next available group of Pages as a source for a Page withina Page Stripe for the data to be stored. This process is illustratedgenerally in FIG. 11.

FIG. 11 generally illustrates the selection of a Page Stripe location ininstances where the Flash controller 10 is already in possession ofinformation identifying a group of blocks in physical memory where datamay be stored. Because the group of Blocks is intended for the storageof Page Stripes, and because there is a general one-to-onecorrespondence between the number of Blocks in the group of Blocks andthe number of Pages in the Page Stripes that are stored in the Blocks,the group of Blocks is referred to herein as a Block Stripe. In theexample of FIG. 11, the Block Stripe is sized to have ten Blocks suchthat the Page Stripes stored within the Block Stripe have nine DataPages and one Data Protection Page.

In Flash memory, it is beneficial to write data into a Blocksequentially, by Page. Thus, when writing to a Block of Flash memory, itis desirable and beneficial to write first to the PAGE0 location, thento the PAGE1 location and so on until the Block is full, or nearly full,of stored data. In the embodiment of FIG. 11, this form of writing isaccomplished by having the Flash controller 10 maintain a count so thatthe first Page Stripe written into a given Block Stripe is writtenacross all of the PAGE0 locations of the Blocks within the Block Stripe,the next Page Stripe across the next page (PAGE1) locations within theBlock Stripe and so on. This is reflected in the illustrated example ofFIG. 12 where it is assumed that the Flash controller 10, at the time itreceived the WRITE operation from the host device, had informationindicating that the Block Stripe had locations available for storage ofa Page Stripe. For purposes of explanation, it is also assumed that PageStripes had already been stored in the PAGE0-PAGE3 locations within theBlock Stripe as reflected in FIG. 12. Thus, in this example, the Flashcontroller would identify the Page Stripe for the PAGE4 locations withinthe Block Stripe as the physical location to which the received datashould be stored.

In the previous example, it was assumed that the Flash controller 10 wasalready aware of a Block Stripe in which data could be stored. Undercertain conditions, the Flash controller 10 will not be aware of a BlockStripe in which data can be stored. This condition can occur, forexample, just after the Flash controller has written a Page Stripe tothe last available page locations of a previously available BlockStripe. Under these conditions, the Flash controller needs a mechanismfor identifying another available Block Stripe to store data.

In one embodiment of the memory system 100 described herein, themechanism for identifying available Block Stripes involves having theFlash controller 10 pull data identifying an available (or free) BlockStripe from a buffer in which locations of Free Block Stripes arestored. This buffer, referred to herein as the Free Block Stripe Buffer,is a buffer that contains, for each entry, information that identifies agroup of Blocks into which data can be stored in a Page Stripe manner.In this embodiment, the entries in the Free Block Stripe Buffer are suchthat all of the Blocks corresponding to an entry have been previouslyerased and are therefore available for the immediate storage of data.

In embodiments where the memory system 100 can store Page Stripes ofdifferent format, the Free Block Stripe Buffer may also contain specificinformation for each entry, or for a group of entries, indicating theformat of the Page Stripes that can be stored in the buffer. Forexample, such entries may indicate that the Block Stripe correspondingto one particular entry of the Free Block Stripes buffer can store PageStripes having nine Data Pages and one Data Protection Page and that theBlock Stripe for a different entry can store Page Stripes having eightData Pages and one Data Protection Page. This formatting information canbe stored as part of the Free Block Stripe Buffer or could be stored ina different buffer. Alternatively, multiple Free Block Stripe Bufferscould be maintained with each one storing Block Stripes capable ofstoring Page Stripes of different formats. In that embodiment, therewould be one Free Block Stripe buffer that stored Free Block Stripescapable of storing Page Stripes having nine Data Pages and one DataProtection Page, another Free Block Stripe Buffer storing Free BlockStripes capable of storing Page Stripes having eight Data Pages and oneData Protection Page and, potentially other Free Block Stripe Buffersstoring Free Block Stripes capable of storing Page Stripes having seven(or even fewer) Data Pages and one Data Protection Page.

In embodiments where there are one or more Free Block Stripe Buffers,each corresponding to Page Stripes of different formats, the Flashcontroller 10 can intelligently decide to select the entry in the FreeBlock Stripe Buffer that would optimize overall performance of thememory system 100. For example, if the Flash controller 10 was awarethat the host device was attempting multiple WRITE operations to thesystem and each WRITE operation was associated with data sufficient tostore nine Data Pages of data, or if the Flash controller 10 wasattempting to move only nine pages of data, the Flash controller couldselect the Free Block Stripe Buffer entry corresponding to a BlockStripe of adequate size to store a Page Stripe with nine Data Pages (andone Data Protection Page). If the Flash controller 10 was aware that thehost device was attempting multiple WRITE operations and all, or asubstantial number of the operations involved quantities of datainsufficient to fill nine Data Pages, or if the Flash controller wasattempting to move less than nine pages of data, the Flash controllercould select an entry from the Free Block Stripe Buffer corresponding toa different Page Stripe format (such as a Page Stripe with eight DataPages and one Data Protection Page). (Move operations are discussed inmore detail below.) In this manner, the overall operation of the systemcould be optimized.

Still further, in some embodiments of the memory system 100 of FIG. 1,the Flash controller 10 could select and have available for storagemultiple Block Stripes. Thus, as long as the received WRITE operationsfrom the host device, or data for a move operation, was such that therewas sufficient data to fill nine Data Pages, the Flash controller couldselect Block Stripes sufficient to store Page Stripes with that numberof data pages. If a WRITE or move operation was such that it did nothave adequate data to fill nine Data Pages, or if the data whenconfigured has a portion that could not fill nine Data Pages, the Flashcontroller 10—to the extent that it did not otherwise have an availableBlock Stripe of that format—could select a Free Block Stripe from theFree Block Stripe Buffers that was of a size appropriate to the amountof data to be stored. This approach could improve the overallperformance of the system because, in the absence of such a step, it maybe necessary to add dummy data (in the form of appended logical 0's or1's) to received data to “fill” out a Page Stripe.

Various approaches and methods for populating the Free Block StripeBuffer(s) are discussed in more detail below.

After an available Page Stripe location is selected, the Flashcontroller 10 will, in some embodiments, configure the data receivedduring the WRITE operation so that it will “fit” into the selected PageStripe location on a Page-aligned basis. This step will involve theFlash Controller 10 breaking up the received data into data groupsappropriate for storage in a Page Stripe, generating the data to bestored in each Data Page of the Page Stripe (including any LBA data, CRCand/or ECC data as discussed above) and also generating the data for theData Protection Page for the Page Stripe (as discussed above). Undercircumstances where the amount of data from the host device that is tobe stored in the Page Stripe is insufficient to fill out all of the DataPages for the Page Stripe, the Flash controller 10 may append logical1's or 0's (or any other data) to the data to be stored so that acomplete Page Stripe of information can be written to the physical PageStripe location.

While this configuration step is described above as following the stepof selecting the Page Stripe location for the storage of the data, theorder of steps could be reversed. In such embodiments, the configurationstep could be used to identify the amount of data that was to be storedin the Page Stripe which could enable the Flash controller 10 to selectthe available Page Stripe location that would minimize or eliminate theneed to append data bits to the stored data to fill out the Data Pagesfor the Page Stripe. Since such appended data bits do not constituteactual host device stored data, the reduction of the extent of theappended bits can enhance overall system performance.

After the data to be stored is configured as described above, theconfigured Page Stripe is written to physical memory. This step involvesthe Flash controller 10 issuing the appropriate commands across thecommunication bus 16 to indicate to the memory storage devices thatwrite operations will occur, to indicate the specific Page locationswhere the write operations will occur and to provide the data for thoseoperations. As noted above, because of the design of the memory system100, the write operation may occur simultaneously or near-simultaneouslyfor the Pages that make up the Page Stripe being stored.

At, after, or prior to the time of the actual writing of the Page Stripedata to physical memory, the Flash controller 10 will update theLogical-to-Physical conversion table to associate each LBA provided bythe host device with the actual physical location at which the datacorresponding to each LBA was stored.

Still other embodiments are envisioned where the Flash controller 10will write data to the memory array 14 on a Page-by-Page basis as datais received from a host device. Thus, as a given Page of data isreceived and a WRITE request is received, the Flash controller willwrite the data to the next Page in the current Page Stripe. In thisembodiment, because data is written as received on a Page-by-Page basis,there is the potential that a READ operation could be requested of aPage before the Page Stripe containing that Page is “filled-out” andbefore the Data Protection Page for the Page Stripe containing the Pageis stored to physical memory.

If a READ operation is received for a Page written in such a manner, theFlash controller can retrieve the data for the requested Page and,assuming that the ECC and CRC data confirms that the Page has valid dataand/or identifies an error that can be corrected through use of the ECCdata within the Page, provide the requested Page of data to the hostdevice. In such a circumstance, there is no need to complete the PageStripe before servicing the READ request. The memory system 100 cansimply service the READ request and wait for the receipt of adequateinformation to complete the Page Stripe at some point in the future.

In the embodiment described above, however, there is a potential thatthe requested Page will have an error associated with it that cannot becorrected using the intra-page ECC and CRC data. In such a scenario, itmay be necessary to utilize the Data Protection Information for theincomplete Page Stripe, which currently resides in the addressable XORmemory buffer associated with that Page Stripe. To do so, the Flashcontroller 10 could: (i) take the accumulated XOR data for the“incomplete” Page Stripe; (ii) modify the format for the Page Stripe atissue so that the modified format includes only the received data as ofthat time (e.g., if only seven Data Pages had been received, themodified Page Stripe format would have seven Data Pages and one DataProtection Page); and (iii) write the then-accumulated XOR data to theData Protection Page for the reformatted Page Stripe. The system couldthen use the complete modified Page Stripe to recreate the data for thePage that was corrupted. The next WRITE operation received by the systemwould then be directed to a different Page Stripe. This approach would,therefore, allow the system to modify and “complete” a Page Stripe anduse the Data Protection Page information for that Page Stripe toregenerate data from a lost or corrupted page without having to either:(a) wait until a Page Stripe of nine Data Pages and one Data ProtectionPage is completed, or (b) complete a ten-Page Page Stripe through thewriting of dummy data (e.g., 0's, 1's or other dummy data).

Populating the Free Block Stripe Buffer(s):

As noted above, depending on the embodiment, one step of the WRITEoperation can involve the Flash controller 10 pulling Free Block Stripeinformation from one or more Free Block Stripe Buffers. The followingdiscusses the manner in which the Free Block Stripe Buffer (or Buffers)can be populated. In one embodiment, the Free Block Stripe Buffer(s)is/are populated through the use of apparatus and methods that:

(i) monitor the memory array to identify Blocks that are in a conditionto be erased;

(ii) place the identified Blocks in one or more buffers that storeinformation concerning Blocks that are ready to be erased;

(iii) monitor the ready to erase buffers to identify Blocks that,according to certain conditions, may be associated with one another toform a Block Stripe;

(iv) upon identifying Blocks that may be associated with one another toform a Block Stripe in accordance with the applied conditions:

(a) move VALID data as may be necessary from the identified Blocks toother physical storage locations;

(b) perform ERASE operations on the identified Blocks once cleared ofVALID data;

(c) associate the identified Blocks with one another to form a BlockStripe that is free and available for data storage; and

(d) place information identifying Free Block Stripes in one or more ofthe Free Block Stripe Buffers (described above).

To understand the following discussion it is helpful to have anunderstanding of certain aspects of a Flash memory device. In general, aparticular Page within a Flash memory device must be completely erasedbefore any data can be written to that Page. As discussed above, theERASE operation typically involves the setting of the bits in aparticular Block of data to a logical 1 state or a logical 0 state.After a Block of Flash memory has been erased, data can be written intothe Pages within that Block. As discussed above, it is beneficial toperform such write operations on a sequential, Page-by-Page basis, suchthat data is first written to the PAGE0 location, then to the PAGE1location, and then continuing sequentially through the pages of theBlock. Because of this aspect of Flash memory, whenever a host deviceattempts multiple WRITES to the same logical address, or LBA, it is notpossible or optimal to write the data associated with that request tothe same physical memory locations. This is because writing to the samephysical Page would first require a lengthy erasure of the block inwhich the Page resides. Thus, in certain embodiments of the systemsdisclosed herein, sequential WRITE operations directed by the hostdevice to the same LBA will commonly and typically involve writeoperations to different physical locations. When this occurs, the datathat was previously stored in the physical location formerly associatedwith the LBA is no longer valid data. It is, as described herein, DIRTYdata, in that it no longer is guaranteed to correspond to the actualvalid data associated with the LBA at issue.

Identification of Blocks that are Ready to be Erased:

Because ERASE operations in Flash memory devices are performed on aBlock-by-Block basis, and because the presence of a DIRTY Page within aBlock does not necessarily indicate the presence of another DIRTY Pagewithin the same Block, it is not optimal to ERASE a Block simply becauseone (or even several) Pages of data become DIRTY. However, it has beendiscovered that it is also not optimal for the memory system 100 to waituntil conditions exist in which the Pages within a given Block becomeDIRTY. This is because such conditions may not occur or, if they dooccur, they occur at intervals that are not optimal for systemperformance. Thus, in certain embodiments of the memory system 100disclosed herein, apparatus and methods are used to monitor the memoryarray to identify Blocks that are in a condition to be erased. Thisidentification is done in a manner that optimizes overall systemperformance.

In this embodiment, the system maintains one or more tables that trackthe DIRTY status of various pages within the system. In one embodiment,one or more tables are maintained that track, for each Block Stripe, thenumber of DIRTY pages within the Block Stripe. In such an embodiment, aBlock Stripe State Table can be maintained, with each entry in the tablecorresponding to a given Block Stripe. Whenever the table indicates thata Block Stripe is sufficiently dirty, the remaining valid data in theBlock Stripe could be written into alternate physical memory locationsthrough a move operation and the LPT table updated to reflect the move.

In some embodiments, a previously erased Block Stripe will be directlyplaced in the Free Block Stripe Buffer. However, in situations where oneor more of the Blocks within the Block Stripe are determined to be bador where a Flash chip or portion of a chip containing the Block Stripeis determined to be bad, the Block Stripe that was erased cannot beused. In such situations new Block Stripes can be assembled from the“good” Blocks of such Block Stripes using one or more Ready-to-EraseBuffers that contain information about Blocks within such Block Stripes.

Assembly of Free Block Stripes Using the Ready to Erase Buffer(s):

In the exemplary memory system 100 of FIG. 1, a beneficial approachinvolving the use of one or more Ready-to-Erase (or “RTE”) Buffers isutilized. In this approach, the memory system 100 maintains one or moreof a number of related Ready-to-Erase buffers in which informationidentifying one or more Blocks of physical memory that are ready to beerased are maintained and in which the system follows a process of usingthe data in the Ready-to-Erase buffer to select blocks of data forefficient Erasing operations.

FIG. 13 illustrates one exemplary set of RTE buffers 1300 that may beutilized with the memory system 100 of FIG. 1. The illustrated set ofbuffers is for a given Chip Enable. The RTE buffers within the set 1300can be maintained as individual buffers, a large arrayed buffer, or acollection of arrayed buffers. The arrangement is not critical as longas the Blocks within the RTE buffer set 1300 can be identified (andselected for association with one another) on a per Lane and per Planebasis. The buffers within set 1300 may be maintained by CPU 15 andstored within a memory location utilized by CPU 15. The buffers withinthe set 1300 may be first-in first-out (or FIFO) buffers.

As noted above, in the example of FIG. 13, the RTE buffers aremaintained on a per Lane and per Plane basis such that the set 1300 ofRTE buffers identifies, at any given time, Blocks of memory that areready to be erased and, for each such Block, the specific Lane and Planeassociated with that Block. Because of this organization, the memorysystem 100 can use the RTE buffers to efficiently perform ERASEoperations to optimize the overall performance of the system 100.

In one embodiment, the CPU 15 within the memory system 100 monitors theinformation in the RTE buffer set 1300 to identify groups of Blockswithin the RTE buffer that are associated with memory locations that canbe used to efficiently store a Block Stripe of data. When such a groupof Blocks is identified, the CPU 15 will execute instructions to: (1)cause an ERASE operation to be performed on the Blocks within theidentified group, and (2) cause one or more indications to be providedthat: (a) associate the Blocks in the identified group with one anotherso that memory locations within the Blocks can be used to store PageStripes of data, and (b) indicate that the Blocks that make up theidentified group are free and available to store data.

Various approaches can be implemented using CPU 15 to identify Blockswithin the RTE buffer set 1300 that are optimal for use in storing PageStripes of data.

For various reasons, it can be beneficial to store the Pages within aPage Stripe of data in memory locations that: (a) are associated withdifferent Lanes and (b) are all within the corresponding Planes.

Exemplary benefits of having the Pages of a Page Stripe correspond todifferent Lanes were discussed above.

One of the benefits of having all of the Pages of a Page Stripe withinthe same Plane is that it allows for the use of faster and potentiallymore efficient operations to move data within the physical memory array.The act of moving data from one physical Page location to another Pagelocation can be accomplished in a variety of ways. One approach for sucha movement of data would be to read the data from the original Page intoa buffer external to the Flash chip where the data originally residedand then WRITE the data into a Page within the same or a different Flashchip. While such an approach accomplishes the ultimate objective ofmoving the data from the original Page location to a new Page location,the approach requires the time and overhead associated with providingthe data external to the Flash chip and writing the data from anexternal location into a location within the same or a different Flashchip. Another approach allowed by many Flash memory chips is to takeadvantage of the fact (generally described above) that the Pages withina given Plane of a Flash chip typically share input/output circuitrythat includes an Input/Output (I/O) Buffer. Because of this sharing ofI/O circuitry, it is possible to move data from one Page within aparticular Plane into another Page within the particular Plane withouthaving to incur the overhead expenses (in terms of time, power, etc.)involved with reading the data to be moved to a location external to thechip and then back into the same or a different chip. Many Flash devicesprovide support for such intra-Plane moves. By ensuring that all of thePages within a given Page Stripe are in the same Plane, the disclosedsystem enhances the ability of the system to ensure that most or all ofthe movements of the data within a Page Stripe (e.g., a move required bya subsequent WRITE to a Page location within a Page Stripe containingdata) are intra-Plane moves that can utilize the faster and moreefficient approach(s) that can be used to implement intra-Plane datatransfers. This is because it would be difficult for the system toidentify destination locations that would allow for each Page of thePage Stripe to be moved via an intra-Plane operation if the Pages withinthe Page Stripe were from different Planes.

In accordance with the teachings of the present disclosure, one approachfor identifying a suitable group of Blocks within the RTE buffer set1300 to obtain the advantages described above would be to monitor theBlocks in the buffer set 1300 to determine when groups of Blocks can beidentified where the Blocks within the candidate group are: (a)associated with physical addresses in different Lanes, and (b)associated with the corresponding Planes. Under this approach, thesystem CPU 15 would execute instructions that associate the Blockswithin the candidate group with one another and that cause an ERASEoperation to be performed on the Blocks within the candidate group.

The precise approach used to determine when sufficient Blocks of datahave been identified that meet the above criteria (e.g., differentLanes, corresponding Planes) can vary depending on the operationalstatus of the memory system 100. For example, when the RTE buffers arepopulated such that the overall set of candidate blocks is uniformlydistributed across Lanes and Planes, then the CPU may simply wait untilthere is one block in each Lane, with each block residing in the samecorresponding Plane. This approach would allow the Page Stripe thatcould be formed from the group of Blocks to have the maximum number ofPages (assuming that each Page of data was to be stored in an addresswith a different Lane association). Because this approach would maximizethe amount of data stored in each Page Stripe, it may be the initiallypreferred approach and, the system 100 may first look for groups ofBlocks within the RTE buffer set 1300 such that: (i) each Block isassociated with a different Lane; (ii) each Block is associated with thesame corresponding Plane; and (iii) the number of Blocks is equal to thenumber of Lanes.

Under certain operating conditions, the population of the Blocks in theRTE buffer set 1300 may be such that it is difficult or impossible forthe system to readily identify a candidate group of Blocks meeting thepreferred criteria described above. This condition could exist, forexample, when one or more of the Flash memory chips that make up thememory array 14 fail. While failures are not common and not expected,they can occur. Thus, it is possible that, for a given memory array 14,one or both of the Flash memory chips associated with a given Lane couldfail. In embodiments where only known-good Blocks are placed in the RTEbuffer set 1300 and where both Flash chips associated with a given Lanefail, the failure of the Flash chips would ensure that no Blocksassociated with that Lane are placed in the RTE buffer. The absence ofBlocks associated with the Lane associated with the failed Flash chipswould ensure that the preferred conditions (where there is a Blockassociated with each Lane) would not occur.

In addition to complete chip failures, partial chip failures couldcreate conditions under which it would be difficult to identifycandidate groups within the RTE Buffer set 1300 that meet the preferredconditions. For example, while complete Flash chip failure is relativelyrare, it is not uncommon for given Blocks within a chip, given Planeswithin a chip, or given CEs within a chip either to fail duringoperation or to be inoperative upon initial use of the chip. Again, inembodiments where only known-good Blocks are placed in the RTE bufferset 1300, these failures can significantly reduce the number of Blocksthat are placed within the RTE buffer set 1300 for a given Lane and/orgiven Plane.

It should be understood that, as used herein, the failure of a chip orthe failure of a portion of a chip can include the actual failure of achip or the occurrence of a situation indicating an anticipated orpredicted failure of a chip or a portion of a chip.

Still further, the manner in which data is written to and/or read fromthe memory array can create conditions under which it is difficult toidentify groups of Blocks in the RTE buffer set 1300 meeting thepreferred conditions.

Under conditions as described above, in which the preferred conditionsfor the selection of groups of Blocks in the RTE buffer set 1300 do notreadily exist, the memory system 100 may operate to select groups ofBlocks that, while not meeting the preferred conditions, meet a firstreduced set of conditions that are appropriate for the operation of thesystem. For example, if the population of Blocks within the RTE bufferset 1300 is such that the system cannot, after a given amount of time oroperational cycles, identify a group of Blocks meeting the preferredconditions, the system may determine whether a group of Blocks meetinganother set of conditions can be identified. For example, if a group ofBlocks cannot be identified where there is one Block associated witheach Lane in the system, the system may determine whether a group of NBlocks can be identified from different Lanes, where N is one less thanthe total number of available Lanes. If such a group of Blocks can beidentified that meets this first reduced set of conditions, the systemcan then associate that group of Blocks together as a location forstoring Page Stripes, where the number of Pages in such Page Stripes isone less than the total number of Lanes in the system, and ensure thatERASE operations are performed on the Blocks within that group.

If the population of the RTE Buffers is such that it is difficult orimpossible for the system to identify groups of Blocks in the RTE bufferset 1300 meeting the first set of reduced conditions, the system couldattempt to identify blocks meeting a second set of reduced conditionssuch as, for example, conditions where there are N′ Blocks that can beidentified, where N′ is two less than the number of available Lanes. Theoperations using this second set of reduced conditions could followthose described above in connection with the first set of reducedconditions. Depending on the system, the system could look for groupsmeeting other sets of reduced conditions, if an inadequate number ofgroups of Blocks meeting the already presented sets of reducedconditions were identified.

In the embodiment described above, the operation of the system in termsof accepting and using groups of Blocks in the RTE buffer set 1300meeting conditions other than the preferred conditions can be static orcan vary depending on the operational state of the memory system 100.For example, during periods where there is little write activityoccurring within the system, such that there is not a great need for alarge number of available Page Stripe locations ready to receive data,the system 100 could operate under conditions where it waits to identifygroups of Blocks meeting the preferred conditions before taking action.During periods where there was a large amount of write activity, suchthat there was a significant need for available Page Stripe locations,the system could more readily process groups of Blocks meeting reducedcriteria. Still alternate embodiments are envisioned where the system100 would be willing to accept groups meeting reduced criteria until adesired inventory of available Page Stripe locations was assembled andthereafter, as long as the inventory was at or near the desiredinventory, utilize the preferred criteria. In such embodiments, thedesired inventory count could be static or variable depending on thewrite activity of the system 100.

It should be noted that the system and methods described above canresult in operation of the system 100 where the data stored in thememory array 14 is stored in Page Stripes having different numbers ofPages and, therefore, different amounts of stored data and differentdata protection information. For example, if the operation of the systemdescribed above resulted in some Page Stripes that include ten pages andothers with nine pages, there would be differences between the amountsof data stored within the Page Stripes (some would have nine Data Pagesand others eight Data Pages) and also differences in the Data Protectionmechanism used to protect the stored data (in one example some DataStripes would have data protected using data protection informationobtained by XORing data from nine Pages of data, while others would usedata protection information obtained by XORing data from eight Pages ofdata).

Exemplary READ Operations:

Having described how WRITE operations may be accomplished using thememory system 100 disclosed herein, and how move operations may be madeto move valid data from one Block that is to be erased into anotherBlock, a general discussion of the manner in which READ operations isperformed shall be provided.

In general, a READ operation is performed when the Flash controller 10receives a READ request from an external host device. In general, theREAD request will comprise a request from a host device to READ a Pageof data associated with a particular LBA provided by the host device. Toperform a READ operation, the Flash Controller will, in one embodiment:

(i) look up the LBA in the Logical-to-Physical translation table toidentify the particular physical address where the Page storing therequested data is located;

(ii) issue a READ request to read the Page of stored data at thephysical location corresponding to the requested LBA;

(iii) validate and, if necessary, correct or reconstruct the requesteddata using the ECC data and/or the information in the Data ProtectionPage for the Page Stripe corresponding to the requested LBA; and

(iv) provide the host device with the retrieved Page of data.

The order of operations set out above is exemplary and embodiments areenvisioned where the order is different from that set out above. Forexample, embodiments are envisioned wherein steps (iii) and (iv) areinterchanged and the data would be provided to the host device followedby an indication of whether the data was valid or not.

In one embodiment, this reading of data is done on a Page specificbasis, where the Page of data that is retrieved corresponds to the Pageof data associated with the LBA provided by the host device. However, ifthe Page of data retrieved as a result of the READ operation isdetermined to be corrupted to a point that it can not be correctedthrough intra-Page ECC and/or CRC (or if the page is determined to havefailed or to be unreadable for any reason) then the Data Pages and theData Protection Page for the Page Stripe in which that Page resides maybe read and used to reconstruct the data within the Page associated withthe LBA provided by the host device.

Response to Chip or Intra-Chip Failures:

Because the system described above will: (a) check the validity of thedata in each retrieved Page of data using the ECC and CRC data for thatpage; and (b) if necessary, use the Data Protection Page informationwithin the Page Stripe where the Page is found to identify and correctPage failures or corruptions that can not be corrected through ECC, itis possible to identify data errors within the Pages that make up a PageStripe. Such data errors can take the form of “soft” errors or “hard”errors. In general, a soft error is induced by transient events thatcause one or more bits of data to be corrupted but that is notindicative of a physical problem with a specific Flash memory storagecell (or groups of cells). True soft errors are substantially random andare typically not uniquely associated with any specific Pages, Blocks orother physical regions of the memory array.

A hard error is a corruption of one or multiple bits of data that iscaused by a physical aspect of the memory storage device. Hard errorscan be caused by a variety of factors including, but not limited to, thephysical failure of components within a given memory chip (such as thefailure of a charge pump), the physical failure of an entire memory chipor the external support structures for that chip (e.g., the breaking ofa power line or an address line to a chip); the physical failure of allor part of a chip as a result of excessive temperature, magnetic field,humidity, etc. In general, because hard errors are related to thephysical structure of a memory system, hard errors are uniquelyassociated with a particular collection of memory chips, a particularmemory chip, or specific physical regions within a chip (such as a ChipEnable region, Plane or Block).

As noted above, data errors can be detected during a READ operationthrough the use of the ECC and CRC data for each Page. In manyinstances, identified data errors can be corrected through the use ofECC algorithms and/or through the use of the Data Protection information(in the event that a single Page exhibits an uncorrectable error). Insuch instances the ECC or Data Protection information can be used torecreate the corrupted data bit or bits, the recreated data can beplaced within a new Page Stripe along with other Pages from the originalstripe; and the new Page Stripe can be written back to the physicalmemory using the corrected data.

In certain embodiments, the memory system 100 will maintain records ofthe identified data errors and the physical structure associated withthose errors. For example, in one embodiment, the memory system 100, andin particular the Flash controller 10, will maintain records reflectingthe number of errors associated with the various Blocks, Planes and,potentially, Chip Enables and Chips within the system. When these countsshow that the number of errors associated with a given Block, Plane,Chip Enable or Chip are above a predetermined threshold, they canindicate that there has been a failure of a given memory chip or of agiven region within the chip (i.e., a given Chip Enable, Plane or Blockwithin a chip). Under such circumstances, the memory system 100 candesignate the Chip (or intra-chip) region as bad or failed bydesignating the Blocks within the chip or region as bad. In thatembodiment, the Blocks that are identified as bad will no longer be usedby the memory system for the storage of data. This can be accomplishedby, for example, (i) not placing the bad Blocks into the RTE Buffer,such that they are not used in the construction of Free Block Stripesand, therefore, would not be used in a Page Stripe for the storage ofdata, or (ii) continuing to place the bad Blocks into the RTE buffer,but doing so under conditions under which the blocks are identified asbad.

In the embodiment where the bad Blocks are placed into the RTE buffer,an indication would be provided so that the system 100 could use thatinformation when assembling Free Block Stripes. For example, if therewere ten blocks that were in the RTE buffer that meet the conditions forbeing grouped together as a Block Stripe but one of the Blocks was a badblock, the system could then proceed to form a Block Stripe from theidentified Blocks that would have ten Blocks, but would provide anindication as to the bad Block such that the Page Stripe format for thatBlock Stripe would only utilize the nine good Blocks.

The ability of the memory system 100 to identify a failed memory chipand/or failed region within a chip; designate the Blocks associated withthe failed chip or region as bad and then adjust the format of the PageStripes in response to the failed chip or region allows the system toadapt to chip or intra-chip failures in such a way that the overalloperation of the memory system is extremely robust. FIGS. 14A-14Dillustrate this point.

Referring to FIG. 14A, an exemplary memory system in accordance withaspects of the present disclosure is illustrated. Like the memory system100 of FIG. 1, the memory system of FIG. 14A includes a Flash controller10, a CPU 15, and a memory array that includes ten Lanes, with each Laneincluding two memory chips. Assuming that all of the blocks within allof the chips are “good” blocks, the system could store data in thememory array using Page Stripes that are formatted such that each PageStripe, or at least the majority of Page Stripes, includes a Page storedin each of the ten Lanes (e.g., a Page Stripe having nine Data Pages andone Data Protection Page). This is generally reflected in FIG. 14B whichshows the standard Page Stripe format for the embodiment of FIG. 14A.

For purposes of the example of FIG. 14C, it is assumed that both of thememory chips associated with a given Lane fail and are no longeravailable to store data. In the illustrated example, it is assumed thatthe failure has occurred with respect to the chips in LANE5. This couldoccur, for example, as a result of a physical failure within the twochips or some damage being inflicted on the address or power lines tothe chips in the Lane. Because of the nature of the described system100, the failure of the chips in LANE5 would be detected and the system100 could change the format of the Page Stripes that are used so that,as the system reads, writes and moves data, the data that was previouslystored in physical locations across chips in all ten Lanes using a PageStripe format with ten pages, is now stored across chips in only nineLanes using a Page Stripe format with nine pages as reflected in FIG.14D. Thus, in this embodiment, no data stored in the memory system 100was lost, and the memory system 100 can self-adapt to the failure andcontinue to perform and operate by processing READ and WRITE requestsfrom host devices. This ability of the described system to self-adaptautomatically on the fly to chip and intra-chip failures makes thememory system disclosed herein extremely rugged and robust and capableof operating despite the failure of one or more chips or intra-chipregions. It also makes the system very user-friendly in that the failureof one, two or even more individual memory chips or devices does notrequire the removal and potential disposal of a previously used memorystorage components.

It should be noted that the reconfiguration or reformatting of the datato change the Page Stripe format to account for chip or intra-chipfailures may reduce the amount of physical memory space held in reserveby the system and available to the system for background operation. Thisreduction, however, is offset by the ability of the system to continueto operate properly in the event of a chip or Intra-chip failure.

Enhanced WRITE and READ Operations:

In the examples described above, each READ or WRITE request issued by ahost device will typically result in the performance of a READ or WRITEoperation on locations within the physical memory array. While suchoperations can fulfill the operational goals of the memory system 100,they may not be optimal because: (i) the actual access of the physicalmemory array takes some amount of time (thus introducing some delay intothe overall system operation), and (ii) the multiple accesses to thememory array tend to degrade the overall lifespan of chips that make upthe physical array since Flash memory chips used to form the physicalmemory array can be subjected to only a finite number of ERASEoperations and the repeated access will result in increased ERASEoperations.

An alternate embodiment of the memory system 100 of FIG. 1 utilizesmethods and apparatus to improve the overall performance and lifespan ofthe system. This is accomplished by having the system monitor theincoming WRITE requests to assess the specific data that the host deviceseeks to write to the memory system.

It has been discovered that many host devices issue a large number ofWRITE commands that request the memory system 100 to write the same datastring to the memory array. For example, experience has shown that it isnot uncommon for a host device to issue a large number of WRITE commandsrequesting the memory system to write data consisting of logical 0's tovarious LBAs or a large number of WRITE commands requesting the memorysystem to write data consisting of logical 1's to various LBAs. It hasalso been discovered that, in various applications, it is not uncommonfor a host device to issue a large number of WRITE commands requestingthat a specific data string be written to various LBAs. This couldoccur, for example, when the host device was asking the memory system tostore data associated with a specific physical measurement, for examplethe flow rate through a specific orifice. In such situations, if thephysical parameter corresponding to the data was relatively constant(e.g., if the flow rate was constant) the host device would likelyrequest that the same data (reflecting measurement of the parameter atdifferent times) be stored at different LBAs.

To increase the performance of the overall memory system, the embodimentdescribed herein utilizes hardware or a software process that firstconsiders, for each WRITE request, whether the data associated with thatWRITE request meets one of a number of predefined criteria. For example,the system could use hardware to determine if the data associated withthe WRITE request consisted of logical 1's or logical 0's. If it weredetermined that the data associated with the WRITE request was withinone of these predetermined categories, then the memory system would notwrite the data to the memory array, but would rather take an alternatecourse as described below.

In the alternate course, the memory system 100 would create an entry inthe Logical-to-Physical Translation table (LPT) that associated the LBAprovided by the host device with a specific Data Identifier. The DataIdentifier would: (a) have the general format of the physical memoryaddress identifier stored in the LPT when the LBA in the table isassociated with data actually stored in memory, but (b) would notcorrespond to any specific physical address in the physical memoryarray. Instead, the Data Identifier would be associated by the systemwith a specific data string such that, for a given LBA entry, thepresence of the Data Identifier would convey the data associated withthe LBA, even though such data was not actually stored in a physicallocation within the memory array, and even though there was no actualphysical memory location in the array associated with the LBA.

This aspect of the present disclosure is generally identified in FIGS.15A-15B. For purposes of illustration, it is assumed that DataIdentifiers have been predetermined that associate certain DataIdentifier information with certain data strings. In the illustratedexample, the Data Identifier FFFFF is associated with a data string oflogical 0's; the Data Identifier FFFFE with logical 1's; and the DataIdentifier FFFFD with alternating logical 0's and 1's (beginning with alogical 1). This is reflected in the Table in FIG. 15A.

FIG. 15B illustrates an exemplary LPT that has multiple entries, eachentry being associated with a specific LBA. In the illustrated example,the addressing of the table is such that an LPT entry is associated witheach LBA presented by the memory system.

FIG. 15B illustrates the situation that would exist if a WRITE operationis requested in which the data associated with the request is logical0's and the WRITE request was directed to LBA 55. As reflected in thisexample, the system would, before executing the WRITE request, analyzethe data associated with the request, and determine that it was logical0's. This could be done through software analysis of the data or throughthe use of a hardware component, such as a comparator or large AND or ORdevice. Once it was determined that the data was logical 0's, the systemwould—instead of actually storing data in the memory array—discard thedata provided by the host device and store the Data Identifierassociated with that data string in the LPT location that would normallystore the physical address where the data associated with thecorresponding LBA was located.

FIG. 15B illustrates the situation that would exist if a subsequentWRITE operation occurred in which the WRITE was directed to LBA 500 withthe data being logical 0's. Here, the system would, using the approachesdescribed above, determine that the data was 0's, discard the dataprovided by the host device, and write the Data Identifier associatedwith the 0's string to the entry in the LPT associated with the LBA 500.Note that in this example, the entries for both LBA 55 and LBA 500 wouldhave the same Data Identifier.

The same process would be followed for WRITE operations associated withdata strings corresponding to other predefined Data Identifiers.

In terms of the WRITE operation, the use of the Data Identifiers asdescribed above is beneficial because it does not result in the actualwriting of data to the physical memory array and does not suffer thewrite overhead (time delay) that would occur if an actual writeoperation occurred. In one embodiment, the LPT table is stored involatile RAM memory and in particular, DDR2 RAM memory. In general, theaccess times required for volatile RAM memory access are faster thanthose required for Flash memory access. Thus, by eliminating the need toactually access the Flash-based memory array, the use of DataIdentifiers can substantially decrease the time seen by the host devicefor the performance of a write operation. Also, by eliminating the needto actually access the Flash memory array, the total number of ERASEoperations can be reduced and the lifespan of the memory arrayincreased.

The use of Data Identifiers also has an impact on READ operations.Specifically, when a READ operation is attempted for an LBA having anassociated Data Identifier, the system 100 will determine that theaccess is to such an LBA and, instead of accessing an actual physicalmemory location within the Flash memory array, will return the datastring associated with the Data Identifier. Depending on the mechanismused to provide the associated data string, the overall READ times seenby the host device may be decreased relative to what would have beenseen had an actual access of the Flash memory array been required.

In the examples of FIGS. 15A-15B, the Data Identifiers were predefinedto correspond to specific anticipated data strings. Alternateembodiments are envisioned in which some of the Data Identifiers are notpredefined to be associated with specific data strings, but are ratherconstructed by the system 100 in response to the actual operation of thesystem

For example, in some embodiments the system 100 can include a processthat runs in the background during relatively idle time, in which thedata actually stored in the memory array is considered. In thisembodiment, if the analysis indicates that there is a sufficiently largenumber of data entries in the memory array corresponding to the samedata string, the system would then define a Data Identifier as beingassociated with that specific data string and would modify thecorresponding LPT entries. This process not only could speed up READ andWRITE requests as described above, it could also free up memory spacewithin the memory array that would otherwise be used to store suchrepetitive data, thus providing more available physical memory andimproving the overall operation of the system.

In an alternate embodiment, the system 100 can include a running DataString Cache memory that associates a Data Identifier with each of themost recent data strings associated with the last N number of WRITEoperations (where N is a predefined number). In this embodiment, if asubsequent WRITE operation uses a data string associated with an entryin the Data String Cache, the Data Identifier will be used for thatentry. A count can be maintained of the number of times a hit occurs forthe entries in the Data String Cache. If it is determined that an entryhas an insufficient number of Hits, then the particular entry can bedeleted from the cache, the corresponding data string actually stored inphysical memory and a physical memory location assigned to each of thecorresponding LBAs in the LPT table. Another data string entry couldthen be placed in the Data String Cache.

The above embodiments are illustrative and not limiting. Other andfurther embodiments utilizing one or more aspects of the inventionsdescribed above can be devised without departing from the spirit ofApplicant's invention.

Further, the order of steps can occur in a variety of sequences unlessotherwise specifically limited. The various steps described herein canbe combined with other steps, interlineated with the stated steps,and/or split into multiple steps. Similarly, elements have beendescribed functionally and can be embodied as separate components or canbe combined into components having multiple functions.

The inventions have been described in the context of preferred and otherembodiments and not every embodiment of the invention has beendescribed. Obvious modifications and alterations to the describedembodiments are available to those of ordinary skill in the art. Thedisclosed and undisclosed embodiments are not intended to limit orrestrict the scope or applicability of the invention conceived of by theApplicants, but rather, in conformity with the patent laws, Applicantsintend to protect fully all such modifications and improvements.

1. A FLASH memory based solid state storage system comprising: (a) aprinted circuit board; (b) a plurality of FLASH memory chips mounted tothe printed circuit board, each FLASH memory chip including a pluralityof FLASH memory cells arranged to store a plurality of pages of digitaldata and a chip-level communications bus interface capable of receivingand sending digital data to be stored in, and retrieved from, FLASHmemory cells within the FLASH memory chip; and (c) a system controllermounted to the printed circuit board, the system controller including aplurality of system communication bus interfaces, each systemcommunication bus interface being coupled by a system communications busto one or more chip-level communication bus interfaces such that thesystem controller can provide digital data to and retrieve digital datafrom memory cells within the one or more FLASH memory chips, the systemcontroller further including an external communications bus interfacecapable of receiving digital data to be stored within the storagesystem; (d) wherein the system controller is configured to store datareceived over the external communications bus in the plurality of FLASHmemory chips in the form of page stripes, each page stripe comprising aplurality of pages of information stored in the FLASH memory chips, eachof the plurality of pages being stored in a FLASH memory chip that isdifferent from each of the FLASH memory chips in which the other pagesof information within the page stripe are stored, the plurality of pagesmaking up each page stripe including: (i) a plurality of data pages, and(ii) at least one data protection page containing data protectioninformation that may be used to reconstruct data stored in a data pagewithin the page stripe that becomes corrupted or unavailable, the dataprotection information for a given page stripe being obtained byperforming a bitwise logical operation on the information within thedata pages for the given page stripe; (e) the page stripes stored by thesystem controller including: (i) a first page stripe stored within theplurality of FLASH memory chips, the first page stripe having N datapages and one data protection page, where N is an integer greater thanthree; and; (ii) a second page stripe stored within the plurality ofFLASH memory chips, the second page stripe having M data pages and onedata protection page, where M is an integer less than N.
 2. The FLASHmemory based solid state storage system of claim 1 wherein each of thedata pages within the second page stripe is stored within a FLASH memorychip that also stores data from a data page within the first datastripe.
 3. The FLASH memory based solid state storage system of claim 1wherein the bitwise logical operation used to obtain the data protectioninformation for each page stripe is the exclusive-or (XOR) operation. 4.The FLASH memory based solid state storage system of claim 3 furthercomprising circuitry for generating the data protection information foreach page stripe by performing XOR operations on data from the datapages within the page stripe.
 5. The FLASH memory based solid statestorage system of claim 1 wherein N is nine.
 6. The FLASH memory basedsolid state storage system of claim 1 wherein the system controller isconfigured such that each data page includes error correction code data,the error correction code data being generated by the system controllerusing data within the page that was initially received over the externalcommunication bus.
 7. The FLASH memory based solid state storage systemof claim 6 wherein the system controller is configured to use the errorcorrection code data within each data page to identify informationwithin a given page that is corrupted or unavailable.
 8. A board-mountedFLASH-based memory storage system comprising: (i) a printed circuitboard; (ii) a plurality of FLASH memory devices, each mounted to theprinted circuit board; (iii) a controller mounted to the printed circuitboard; and (iv) a plurality of communications buses, each configured toallow the controller to write a data collection to one or more FLASHmemory devices; (v) wherein the controller is configured to write datato the FLASH memory devices in a striped fashion using data stripes,where each data stripe includes a group of data collections and anassociated set of data protection information such that: (a) each datacollection within a group of data collections is written into a FLASHmemory device that differs from (1) the FLASH memory devices into whichthe other data collections within the group of data collections arewritten and (2) the FLASH memory device to which the data protectioninformation associated with the group of data collections is written;(b) each data collection includes error correction code data generatedfrom the data stored in the data collection; and (c) each set of dataprotection information is generated by performing a bitwise exclusive-or(XOR) of the data within the data collections associated with the set ofdata protection information; (vi) wherein the controller is adapted touse the error correction code data within each data collection toidentify an error within the data collection; (vii) wherein thecontroller further includes circuitry for using the set of dataprotection information to reconstruct the data for a data collectionassociated with the set of data protection information; and (viii)wherein the controller is configured such that the number of datacollections within the group of data collections can vary.
 9. Theboard-mounted FLASH-based memory storage system of claim 8 where thenumber of bits in each data collection is equal to the number of bits ineach set of data protection information.
 10. The board-mountedFLASH-based memory storage system of claim 8 wherein the controller is afield programmable gate array including circuitry for calculating thebitwise XOR of a plurality of data collections within a group of datacollections.
 11. The board-mounted FLASH-based memory storage system ofclaim 8 further including a first group of M data collections stored inthe plurality of FLASH memory devices and a second group of N datacollections stored in the plurality of FLASH memory devices, where M isan integer number greater than three and where N is less than M.
 12. Theboard-mounted FLASH memory storage system of claim 11 wherein there are0 FLASH memory devices, where 0 is an integer greater than M.
 13. Theboard-mounted FLASH-based memory storage system of claim 12 wherein thenumber of communications buses is equal to 0 divided by two.
 14. Theboard-mounted FLASH-based memory storage system of claim 8 wherein eachof the plurality of FLASH memory devices is a FLASH memory chip, andwherein each FLASH memory chip is surface mounted to the printed circuitboard.
 15. A memory system comprising: a plurality of FLASH memorychips, each of the plurality of FLASH memory chips capable of storing apredefined number of bits of information; a system controller coupled tothe FLASH memory chips, wherein the system controller writes informationto the FLASH memory chips using data stripes; a first data stripe storedin the plurality of FLASH memory chips, the first data stripe includingM data pages and a data protection page, where M is an integer greaterthan three and wherein information stored in the data protection pagefor the first data stripe was generated through the performance of agiven operation on information stored within the M data pages of thefirst data stripe; and a second data stripe stored in the plurality ofFLASH memory chips, the second data stripe including N data pages and adata protection page, where N is an integer less than M, and whereininformation stored in the data protection page for the second datastripe was generated from the performance of the given operation oninformation stored within the N data pages of the second stripe.
 16. Thememory system of claim 15 wherein the given operation is a bitwiseexclusive-or (XOR) operation.
 17. The memory system of claim 15 whereineach data page within the first data stripe is stored in a FLASH chipthat is different from the FLASH chips in which the other data pageswithin the first data stripe are stored.
 18. The memory system of claim17 wherein each data page within the second data stripe is stored in aFLASH memory chip that is different from the FLASH memory chips in whichthe data pages within the second data stripe are stored.
 19. The memorysystem of claim 15 wherein the number of bits of information stored ineach data page of the first data stripe is the same and wherein thenumber of bits of information stored in each data page of the seconddata stripe is the same as the number of bits of information stored ineach data page of the first data stripe.
 20. The memory system of claim19 wherein the number of bits of information stored in the dataprotection page for the first data stripe is the same as the number ofbits of information stored in the data protection page for the seconddata stripe.